Web cleaner apparatus and method

Abstract: An apparatus (20) and method for cleaning a moving web (10) of sheet material. The apparatus includes a Coanda nozzle having an elongated, curved foil (22) and a slit (26) for directing gas at a high rate of speed along the foil. The gas from the foil impacts a layer of air entrained by the web of sheet material (10) flowing in an opposed direction. Impact occurs within a gap formed between the foil and the web (10) which becomes increasingly restricted in the direction of movement of the web. The entrained layer of air is caused to reverse direction within the gap and is mixed with the gas from the nozzle under turbulent conditions to clean the web and remove particulate material such as dust therefrom.

Description: This invention relates to a system for cleaning webs of sheet material. More particularly, the apparatus and method of the present invention have application to removing dust and other particulate matter in an entrained boundary layer carried along by fast moving paper or other webs. Such dust and other particulate matter is hereafter generally referred to as detritus. Many arrangements exist in the prior art for cleaning moving webs such as paper webs. Dust and other entrained particles are often carried along by such webs and can present health and safety problems as well as quality control problems. US-A-4 887 623 discloses a method and apparatus for removing particles from a flexible sheet. The sheet is run over a rotating rod, rotating in a direction opposite to the running direction of the flexible sheet. The lower side of the rod is immersed in a bath of solvent to which particles of dust carried along in an air flow associated with the sheet adhere. The dust is delivered therefrom into a slit in which a negative air pressure exists. US-A-3 956 760 discloses a method and apparatus for removing dust from the surface of a moving web in which the surface of the web is washed with a fountain-type washer supplying washing liquid, the liquid on the web being subsequently removed by a high pressure blower and pump mechanism. It will be appreciated that dust and other particles must be quickly and positively removed from fast moving webs such as those found in paper making and paper conversion facilities. The arrangement of the present invention accomplishes this objection in a highly efficient, relatively low cost manner. One of the components of the present system is a Coanda nozzle of specialised construction which is positioned relative to the web in a particular manner which provides a highly turbulent interface between air flow from the nozzle and the entrained layer of air moving with and bordered by the moving web. While it is known generally to deploy one or more Coanda nozzles along the path of a moving web to treat the web in some manner or direct movement of the web, the arrangement of the present invention incorporates structure and method steps which cooperate in a unique manner to effectively and positively clean even very fast moving webs. In one aspect the invention provides a method of cleaning the surface of a longitudinally moving web having an entrained boundary layer comprising disposing an elongated curved surface adjacent the web transversely of the movement thereof characterised in that the surface defines with the web a gap converging in the direction of web movement, the method further comprising supplying a flow of gas to the surface so that it attaches thereto by means of the Coanda effect and passes into the gap in the opposite direction to the web movement, impacting the gas flow upon the said boundary layer, the gas flow having sufficient energy to disrupt the boundary layer and effect turbulent mixing, and removing away from the web the disrupted boundary layer together with detritus therein. In another aspect the invention provides apparatus for cleaning the surface of a longitudinally moving web having an entrained boundary layer comprising: a curved surface, means for mounting the curved surface so as to extend across the width of the web characterised in that said curved surface is elongated in the plane of its curvature, said curved surface and said web together defining a gap converging in the direction of web movement, said apparatus further comprising gas supply means for supplying a flow of gas to the curved surface, so that it attaches to the curved surface by means of the Coanda effect, and passes into the gap in the opposite direction to the web movement with energy sufficient to disrupt the said boundary layer upon impact therewith and effect turbulent mixing, and means for removing away from the web the detached boundary layer together with detritus therein. In a preferred embodiment the apparatus of the present invention is for use in combination with a web of sheet material moving in a predetermined direction along a predetermined path of movement. The web of sheet material has spaced edges and a substantially planar surface bordering a layer of air entrained by the web of sheet material and moving in the predetermined direction. The apparatus is for cleaning the substantially planar surface and includes a Coanda nozzle in a preferred form comprising an elongated curved foil and slit defining means defining an elongated, narrow slit with the elongated curved foil. The elongated, narrow slit is for receiving a compressed gas and directing the gas at a high velocity along the elongated, curved foil from an upstream location on the elongated, curved foil and past an intermediate location on the elongated, curved foil to a downstream location at an end of the elongated, curved foil. The Coanda nozzle is positioned closely adjacent to the substantially planar surface of a moving web of sheet material with the downstream location of the elongated, curved foil being further from the substantially planar surface than is the elongated, curved foil intermediate location whereby the elongated curved foil forms a gap with the moving web substantially planar surface which becomes increasingly restricted in the predetermined direction and within which a layer of air entrained by the moving web of sheet material is impacted by gas flowing at a high velocity along the curved foil in a direction generally opposed to the predetermined direction, mixed with the gas under turbulent conditions and caused to substantially reverse direction away from the curved foil. The curved discharge plate has an elongated entry end location at the Coanda nozzle and extending along the length of the Coanda nozzle. The curved discharge plate elongated entry end is offset from the elongated curved foil downstream location along the length of the Coanda nozzle and located further away from the substantially planar surface of a moving web when the Coanda nozzle is adjacent thereto than is the elongated, curved foil downstream location to promote turbulence of the gas and entrained air layer in the gap. In preferred embodiments, the elongated narrow slit has a substantially uniform width within the range of from about 0.051mm (0.002 inches) to about 0.51mm (0.02 inches), the compressed gas has a pressure within the range of from about 13.8kPa (2 psig) to about 69.0kPa (10 psig) prior to flowing through the slit, and the compressed gas exits the slit at a speed within the range of from about 151m/s (29,800 fpm) to about 338m/s (66,600 fpm). Other features, advantages, and objects of the present invention will become apparent with reference to the following description and accompanying drawings. Fig. 1 is a perspective view of apparatus constructed in accordance with the teachings of the present invention in operative association with a moving web; and Fig. 2 is a cross-sectional side view of the apparatus disposed under a moving web. Referring now to the drawings, a web of sheet material, more particularly a paper web 10, is illustrated as moving in a predetermined direction along a predetermined path of movement indicated by the arrow. Web 10 has spaced edges 12, 14 and a substantially planar surface 16 bordering a layer of air 18 (the lower limit of which is denoted by dash lines in Fig. 2) entrained by the web and moving in the same predetermined direction. It will be appreciated that layer 18 often includes dust and other particulate matter generated during manufacturing or conversion processes. It is the function of the apparatus constructed in accordance with the teachings of the present invention to quickly and efficiently remove such substances from association with the web. Proper cleaning of the web is particularly imperative in those situations wherein the dust or particulate materials represent health or safety problems, as is often the case. For example, dust and other particles, in the absence of proper web treatment, can cause respiratory problems or have the potential for fire or even explosion. The apparatus 20 of the present invention includes a Coanda nozzle having an elongated, curved foil 22 and a housing 24 defining an elongated, narrow slit 26 with the elongated, curved foil. The interior of housing 24 is connected to a source of pressurized air or other gas. The pressurized air or other gas exits slit 26 at a high rate of speed, attaching itself to the elongated, curved foil 22 as a result of the Coanda effect. Such gas movement will also serve to entrain ambient air at the location of the Coanda nozzle whereby the gas and ambient air entrained thereby will move from the upstream location on the foil located at the slit and past an intermediate location on the foil-closely adjacent to the moving web to a downstream location at the end 28 of the elongated, curved foil. This will result in impact by the gas and ambient air entrained thereby on the layer of air 18 entrained by web 10. In other words, the flow or direction of movement of air boundary layer 18 will be in opposition to the direction of movement of the gas and entrained ambient air along the foil surface. It will be noted that the curved foil downstream or end location 28 is further from the substantially planar surface 16 of the web 10 than is the elongated, curved foil intermediate location. Thus, the elongated, curved foil forms a gap 30 with the moving web 10 substantially planar surface which becomes increasingly restricted in the predetermined direction of movement of the web 10. The layer of air entrained by the moving web of sheet material is impacted by the gas and ambient air flowing at a high rate of speed along the curved foil within the gap 30. This results in mixing of the layer of air, gas, and air entrained thereby under turbulent conditions and causes the layer of air 18 to reverse direction away from the curved foil. Since the turbulence adjoins the planar surface 16, a scouring or cleaning action takes place ensuring removal of loose particulate matter from association with the web planar surface. The apparatus of the present invention also includes an air discharge chute 34 which it utilized to direct the gas and particulate mixture away from the Coanda nozzle to a predetermined location. For example, the mixture may be directed to a filter (not shown) for filtering out the particulates. Preferably, a vacuum is applied to the air discharge chute by an exhaust blower or other suitable vacuum means to ensure transport of the gas-particulate mixture to the desired remote location. Discharge chute 34 includes a curved, discharge plate 36 adjacent to the elongated, curved foil 22 and curving away from the Coanda nozzle. The curved, discharge plate 36 has an elongated entry end 38 located at the Coanda nozzle and extending along the length of the Coanda nozzle. The curved discharge plate elongated entry end 38 is offset from the elongated, curved foil downstream location along the length of the Coanda nozzle and located further way from the substantially planar surface of the moving web than is the elongated, curved foil downstream location 28. It has been found that the step formed by this arrangement promotes turbulence of the gas, entrained ambient air, and entrained air layer in the gap. In turn, this contributes to the cleaning efficiency of the apparatus. To the extent that some of the high velocity gas flow remains attached to the curved surface of the Coanda nozzle after impact with the boundary layer 18, this flow serves to entrain the disrupted boundary layer and encourage its movement away from the web towards the discharge chute 34. The Coanda nozzle and air discharge chute extend all the way across the web of sheet material from edge 12 to edge 14. That is, the primary axis of the Coanda nozzle is disposed at substantially right angles to the predetermined direction of the web. For efficient operation of the apparatus, the elongated, narrow slit 26 has a uniform width within the range of from about 0.051mm (0.002 inches) to about 0.51mm (0.02 inches), and even more preferably a width of about 0.25mm (0.01 inch). It is also important that the compressed gas employed for operation of the Coanda nozzle is pressurized within a range of from about 13.8kPa (2 psig) to about 69.0kPa (10 psig) prior to flow thereof through the slit. Even more preferably, the compressed gas has a pressure of about 34.5kPa (5 psig). In operation, the gas exits the slit and flows along at least the upstream end of said elongated, curved foil surface at a speed within a range of from about 151m/s (29,800 fpm) to about 338m/s (66,600 fpm). Operation of the nozzle within such range significantly contributes to the efficiency of the apparatus in cleaning the web and should be compared with prior art devices wherein gas flow speeds and gas pressures are significantly less as well as less effective. While the present invention has been described in its preferred embodiments, it is to be understood that the words which have been used are words of description rather than limitation and that changes may be made to the invention without departing from its scope as defined by the appended claims.

Claims: Apparatus for cleaning the surface of a longitudinally moving web (10) having an entrained boundary layer (18) comprising: a curved surface (22), means (24) for mounting the curved surface so as to extend across the width of the web, characterised in that said curved surface is elongated in the plane of its curvature, said curved surface (22) defines with said web (10) a gap (30) converging in the direction of web movement, said apparatus further comprising: gas supply means for supplying a flow of gas to the curved surface (22) so that it attaches to the curved surface by means of the Coanda effect and passes into the gap in the opposite direction to the web movement with energy sufficient to disrupt the said boundary layer (18) upon impact therewith and effect turbulent mixing, and means (34) for removing away from the web the detached boundary layer together with detritus therein. Apparatus according to Claim 1, wherein the means for supplying the flow of gas is adapted to supply said gas to a portion of the curved surface (22) so that it entrains ambient gas before impacting upon the boundary layer (18). Apparatus according to Claim 2, wherein the curved surface (22) is such as to define said gap (30) in a convergent-divergent form with the web (10), the gas supply means supplying the flow of gas to the divergent part of the gap (30). Apparatus according to Claim 1, wherein the gas remains attached to the curved surface (22) after passing through the throat of the gap and assists in removing the disrupted boundary layer by entrainment thereof. Apparatus according to any preceding claim in combination with a web of sheet material (10) having spaced edges (12,14) and a substantially planar surface (16) and an entrained boundary layer (18) wherein said apparatus comprises: a Coanda nozzle including said curved surface (22) in the form of an elongated, curved foil and slit defining means defining an elongated, narrow slit (26) with said elongated, curved foil for receiving said gas at a high velocity along said elongated, curved foil from an upstream location on said elongated, curved foil and past an intermediate location on said elongated, curved foil to a downstream location at an end (28) of said elongated, curved foil, means for positioning said Coanda nozzle closely adjacent to the substantially planar surface of said moving web of sheet material with the downstream location on said elongated, curved foil being further from the substantially planar surface than is the elongated, curved foil intermediate location to define said gap (30), said detached boundary layer being caused to substantially reverse direction away from said curved foil. The apparatus according to Claim 5, wherein said means (34) for removing away from the web the detached boundary layer together with detritus therein comprises an air discharge chute (34) and means for applying a vacuum to said air discharge chute to direct the detached boundary layer to a location away from said Coanda nozzle, said discharge chute including a curved discharge plate (36) adjacent to said elongated, curved foil (22) and curving away from said Coanda nozzle. The apparatus according to Claim 6, wherein said curved discharge plate (36) has an elongated entry end (38) located at said Coanda nozzle and extending along the length of said Coanda nozzle, said curved discharge plate elongated entry end (38) being offset from said elongated, curved foil (22) downstream location along the length of said Coanda nozzle and located further away from said substantially planar surface (16) of said moving web (10) when said Coanda nozzle is adjacent thereto than is said elongated, curved foil (22) downstream location to promote said turbulent mixing of the gas and entrained boundary layer (18) in said gap (30). An installation comprising means for moving an elongated web longitudinally of itself, and means disposed adjacent the path of the web for cleaning a surface thereof, said means being according to any preceding claim. A method of cleaning the surface of a longitudinally moving web having an entrained boundary layer (18) comprising disposing an elongated curved surface (22) adjacent the web transversely of the movement thereof characterised in that the surface defines with the web (10) a gap (30) converging in the direction of web movement, the method further comprising supplying a flow of gas to the surface so that it attaches thereto by means of the Coanda effect and passes into the gap (20) in the opposite direction to the web movement, impacting the gas flow upon the said boundary layer (18), the gas flow having sufficient energy to disrupt the boundary layer (18) and effect turbulent mixing, and removing away from the web the disrupted boundary layer together with detritus therein. A method according to Claim 9, wherein said web comprises sheet material having spaced edges (12,14) and a substantially planar surface (16) bordering said boundary layer (18), said gas comprises compressed gas supplied through an elongated, narrow slit (26); said elongated curved surface comprises an elongated curved foil surface, said gas flowing along said elongated, curved foil surface at a high velocity, ambient air being entrained with said flowing gas as said gas flows along said elongated, curved foil surface at a high velocity; and substantially simultaneously with said mixing step, said boundary layer being caused to substantially reverse direction away from said elongated, curved foil surface. The method according to Claim 10, including the additional step of applying a vacuum to the mixture of boundary layer, gas and ambient air to direct the mixture to a predetermined location spaced from both said web of sheet material and said elongated, curved surface. The method according to Claim 11, wherein said mixture is directed along a curved discharge surface (36) curving away from the elongated, curved foil surface (22), said curved discharge surface having an entry end (38) offset from said elongated, curved foil surface and located further away from the substantially planar surface (16) of the moving web than is said elongated, curved foil surface to promote turbulence of the mixture in said gap (30).

Inventors: POLLOCK RODNEY E, POLLOCK, RODNEY E.
Applicants: FORT JAMES CORP, FORT JAMES CORPORATION
Application year: 1994
Main classification: B08B1
IPC codes: B08B5